A REVIEW ON IMPURITY TRANSPORT IN DIVERTORS

Power exhaust is one of the most crucial requirements for future fusio n reactors, like ITER. It is widely recognized that impurity injection is needed to significantly reduce the heat load to the divertor plate s. By controlled injection of Light impurities, the compatibility of h igh confinement core plasma with strong radiative divertor has been su ccessfully demonstrated in many tokamaks. However, the core impurity c ontamination was high (Z(eff) similar to 3) compared to the Value requ ired for ITER (Z(eff) < 1.6). Therefore, a scheme for impurity retenti on in the divertor region should be established for fusion research. T his paper reviews the recent progress in experiments and simulations w hich have been made for the purpose of understanding impurity transpor t in diverters. The issues contained in the paper are impurity generat ion, shielding and cross field diffusion. As for the impurity generati on, chemical sputtering and wall source are discussed with emphasis on the characteristics of their transport and shielding. Impurity contro l with plasma flow induced by gas puffing and divertor pumping, and ad equately designed divertor geometry is also presented.